I don't think 9 weeks old is late at all! I think a real chuckle laugh happens closer to 3 months or even later. Both of mine would do little kind of smiles with a grunting sound before that, I suppose that is laughing, but not real giggles until about 14 weeks or so.

I think my DD laughed out loud for the first time when she was about 12 weeks old. But she rarely laughs out loud. She is totally normal developmentally, but she has a reserved personality and just doesn't do much giggling, shrieking, yelling, laughing, or crying when other people are around.

Now at 2 years old she is much more expressive, but she still clams up when we are around a big group of people or strangers.